1. Field of the Invention
The present invention relates to a small size thin type antenna to be equipped with a radio terminal, a multilayered substrate, a high frequency module, and a radio terminal mounting them for providing a user with multimedia services ubiquitously, and more particularly, to a small size thin type antenna, a multilayered substrate, a high frequency module, and radio terminal mounting them, for realizing information transmission by the medium of electromagnetic wave having a wavelength greater than dimensions of the radio terminal.
2. Description of the Related Art
In recent years, various radio terminals have been developed and put into practical use to provide a user with various kinds of information transmission services ubiquitously. Since these services have been diversified year by year into various services, for instance, telephone, television, and local area network (LAN), the user should possess radio terminals corresponding to the respective services for enjoying all services.
So as to improve the convenience of the user enjoying such various services, the realization of a so-called “multimode terminal (multimedia terminal)”, which can complete a plurality of the ubiquitous information transmission services by a single terminal, becomes a great social need.
Use of electromagnetic wave media provides the ubiquitous information transmission services for a normal radio communication. Therefore, it is necessary to employ one frequency for providing one kind of service to provide plural services to the user in a same coverage area.
Accordingly, for the multimedia terminal, a function for transmitting and receiving electromagnetic waves of the plural frequencies is required.
One of key devices for such a multimedia terminal is a multimode antenna having sensitivity for the electromagnetic waves of plural frequencies.
The multimode antenna is an antenna with a single configuration, which provides an excellent matching property between a characteristic impedance of a high frequency circuit in the radio terminal and a characteristic impedance of a free space for the electromagnetic waves of the plural frequencies.
A frequency band to be covered by the multimode antenna has been broadened in accordance with the various services required by the user, such that the frequency range is much lower than a frequency band (800 MHz to 2 GHz) used in the conventional wireless phone. Particularly, a need for realizing broadcasting services for the mobile radio terminal other than the telecommunication rises in recent years. Therefore, there is a requirement for the antenna, which has sensitivity for a frequency band lower than that for the wireless phone, for instance, a frequency band of 200 to 600 MHz.
A wavelength of such a low frequency wave is 0.6 to 1.8 m, which is remarkably greater than dimensions of the mobile radio terminal. Therefore, it becomes difficult to provide the mobile phone terminal with a ¼ to ½ wavelength of the radio wave, which corresponds to an effective electrical length of the antenna required for receiving this radio wave.
For overcoming the above described disadvantage, the prior art, for instance, Japanese Patent Laid-Open (Kokai) No. 1-158805 (JP-A-1-158805) proposes an aerial wire (antenna) , in which a conductor emitting a radio wave is formed within a bulk dielectric material, and an electrical length of the antenna is made to be greater than a physical length of the radiating conductor by utilizing a wavelength compaction function of the dielectric material, thereby realizing equivalently an antenna with a greater electrical length in a mobile radio terminal with smaller physical dimensions.
However, since a three-dimensional dielectric bulk element is used in this prior art, it is necessary to provide a height greater than a predetermined height (0.5 to 0.8 mm) in a vertical direction viewed from a circuit board of the mobile radio terminal to be used. Accordingly, there is a disadvantage in that the antenna according to this prior art is not suitable for sliming the mobile radio terminal, so that it becomes a great obstacle for another need in the user's convenience, namely, the improvement in portability by sliming of the device.
In addition, since the bulk element is used for the antenna, when realizing a high frequency module including this antenna as an essential element, a flexibility of the high frequency module will be remarkably decreased. Accordingly, the high frequency of the module and the mounting configuration for the radio device are largely limited, so that it becomes a great obstacle for development of the device and decrease of fabrication steps due to the decrease in freedom of device design and fabrication method.